I was trading Rishiroop, a rubber sector stock on BSE today. I placed a market order for just 1 stock, but the order immediately got converted to a limit order Rs. 79.5, which was the LTP at that point. Shouldn’t a market order execute immediately? Why did this happen?

Ideally, a market order should execute at the best bid or offer. But in case the stock that you’re placing the order for has hit upper or lower circuit, or has no bids/offers just due to a lack of liquidity, your market order would be converted to a limit order at the last traded price and stay open at the exchange.

In the example you’ve quoted, Rishioop had no buyers or sellers. Check this screenshot of the marketdepth from the BSE website:

In the case of Rishiroop today, when a buy market order was placed, there were zero sellers at that point in time. When this is the case, the market order converts into a limit order with limit price = last traded price.
The reason it converts is because of this: The upper circuit limit for Rishiroop was 95.85 today. Imagine you placed a market order after seeing that the LTP was 79.70. Now if your market order remained open in the system even though there was no seller and then a new seller comes and places a sell limit order at 95, your buy market order should execute at 95. To avoid this danger, it converts to a limit order.

Also, when a stock hits upper circuit limit, there will be only buyers and no sellers. So if you place a buy market order in a stock which has already hit upper circuit, this market order will also convert to a limit order with limit price = upper circuit price.

I am asking about the why my market order sits in the system as a limit order for the stock(recent example Rcom) because as per the price band my order have to execute at market price right?
please correct me if i am wrong.

If a buy market order is placed when a stock is at upper circuit and before the price band is released, the market order converts into a buy limit order at the upper circuit price. If this order is unexecuted once the price band increases, then you have to manage your limit order price accordingly.